U.S. patent application number 10/467855 was filed with the patent office on 2004-06-17 for method and system for interference measurements in a telecommunication system.
Invention is credited to Hedlund, Anders, Sundberg, Krister.
Application Number | 20040116123 10/467855 |
Document ID | / |
Family ID | 20283215 |
Filed Date | 2004-06-17 |
United States Patent
Application |
20040116123 |
Kind Code |
A1 |
Sundberg, Krister ; et
al. |
June 17, 2004 |
Method and system for interference measurements in a
telecommunication system
Abstract
The present invention relates to an apparatus and a method for
measuring interference levels in a telecommunication system
comprising a radio base station communicating with at least one
in-house mounted transceiver, the transceiver defining a
communication range in which it is responsible for handling,
communication terminals, such as mobile phones or computer
terminals. By means of at least one scanner the apparatus
synchronises with transmitted information from the base station to
the transceiver in a time regime. The scanner is connected to
measurement means for measuring the interference level on
transmitted information and the measurement means is adapted to
compare measured interference levels with each other an thereby
improve transmission between the base station and the transceiver
on a favourable frequency, whereby the problem of interference on
allocated traffic channels is alleviated.
Inventors: |
Sundberg, Krister;
(Stockholm, SE) ; Hedlund, Anders; (Skelleftea,
SE) |
Correspondence
Address: |
BURNS DOANE SWECKER & MATHIS L L P
POST OFFICE BOX 1404
ALEXANDRIA
VA
22313-1404
US
|
Family ID: |
20283215 |
Appl. No.: |
10/467855 |
Filed: |
February 5, 2004 |
PCT Filed: |
March 6, 2002 |
PCT NO: |
PCT/SE02/00391 |
Current U.S.
Class: |
455/450 |
Current CPC
Class: |
H04B 17/345 20150115;
H04W 16/20 20130101; H04W 16/18 20130101 |
Class at
Publication: |
455/450 |
International
Class: |
H04Q 007/20 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 6, 2001 |
SE |
0100740-0 |
Claims
1. An apparatus for measuring interference levels in a
telecommunication system comprising a radio base station (40)
communicating with at least one in-house mounted transceiver (30,
32), the transceiver (30, 32) defining a communication range in
which it is responsible for handling communication terminals (60,
62), such as mobile phones or computer terminals, characterised in
that at least one scanner (10, 12) is provided with means for
synchronising with transmitted information from the base station
(40) to the transceiver (30, 32) in a time regime; the scanner (10,
12) is connected to measurement means (not shown) for measuring the
interference level on transmitted information; and the measurement
means (not shown) is adapted to compare measured interference
levels with each other and thereby improve transmission between the
base station (40) and the transceiver (30, 32) on a favourable
frequency.
2. An apparatus in a telecommunication system according to claim 1,
characterised in that after synchronisation, the scanner (10, 12)
is adapted to switch over from a first monitored frequency to a
second monitored frequency.
3. An apparatus in a telecommunication system according to claim 2,
characterised in that the first monitored frequency is a broadcast
control channel (BCCH) carrier and the second monitored frequency
is a traffic channel (TCH).
4. An apparatus in a telecommunication system according to anyone
of the preceding claims, characterised in that a plurality of
communication ranges, i.e. cells, in which one transceiver each is
responsible for handling communication terminals (60, 62), are
grouped together into associations of cells.
5. An apparatus in a telecommunication system according to claim 1,
characterised in that the at least one scanner (10, 12) of the
associated cell is placed on one of the building projections where
the interference situation is difficult.
6. An apparatus in a telecommunication system according anyone of
the preceding claims, characterised in that a scanner manager (not
shown) is adapted to handle measurement information from each
scanner (10, 12) and forward the information to evaluation means
(not shown).
7. An apparatus in a telecommunication system according to anyone
of the preceding claims, characterised in that a filter (not shown)
is adapted to stabilise measurement values before presentation.
8. An apparatus in a telecommunication system according to claim 7,
characterised in that the filter (not shown) being an exponential
recursive filter is adapted to stabilise measurement values before
presentation.
9. A method for measuring interference levels in a
telecommunication system, comprising a radio base station (40)
communicating with at least one in-house mounted transceiver (30,
32), the transceiver (30, 32) defining a communication range in
which it is responsible for handling communication terminals (60,
62), such as mobile phones or computer terminals, the method
characterised by the steps of: synchronising at least one scanner
(10, 12) in a time regime with transmitted information from the
base station (40) to the transceiver (30, 32); measuring the
interference level on transmitted information; and comparing
measured interference levels with each other and thereby improving
transmission between the base station (40) and the transceiver (30,
32) by utilising a favourable frequency.
10. A method for measuring interference levels in a
telecommunication system according to claim 9, further
characterised by the step of: switching over from a first monitored
frequency being a broadcast control channel (BCCH) carrier to a
second monitored frequency being a traffic channel (TCH).
11. A method for measuring interference levels in a
telecommunication system according to claim 9, further
characterised by the step of: measuring the interference level of
transmitted information being both allocated traffic channels (TCH)
and non-allocated traffic channels.
Description
TECHNICAL FIELD OF THE INVENTION
[0001] This invention generally relates to a method and system for
measuring interference in a telecommunication system. More in
particular, the invention relates to interference measurements
primarily, but not exclusively, on allocated and non-allocated
traffic channels.
BACKGROUND OF THE INVENTION
[0002] The last few years, integration of data communication and
telecommunication technologies has been discussed among people, who
used to work in either of the technical fields. The integrating
phenomenon is also known as the convergence of communication
technologies, and a lot of effort is currently put down in
scientific communities and in global research and development
organisations for realising the concept of the Wireless Internet, a
way of accessing information contained within the Internet no
matter when and where the information is to be accessed.
[0003] One way of realising the concept of immediate and constant
access to the Internet in office buildings without cables and wires
that limit the dynamics of the office, is to combine wireless radio
communication technology, such as the GSM, with an Internet
protocol (IP) based local area network (LAN) environment. Such
systems already exist today, although in most cases they are not
yet fully operative. The functionality of such systems may be
similar to that of GSM, but it includes utilisation of Internet
protocol transmission, instead of prior art transmission
technologies.
[0004] Physical properties of radio transmission depend on many
constantly changing parameters. Network and frequency planning must
be performed regularly, and often manually in order to maintain a
functional telecommunication system. Another reason for planning
networks is to avoid internal and external conflicts between
interfering radio channels leading to poor transmission performance
and cut-offs. Predicting the radio transmission in a network by
calculating the properties or by estimating them can be very
complex in many environments, and in-house radio transmission is no
exception. The in-house situation is rather the reverse, since
radio transmission properties change rapidly inside a building, due
to additional irregularities that repeatedly require measurements
and maintenance of allocated frequencies. Due to the difficulties
in maintaining favourable conditions over longer periods of time
for radio transmission, physical conditions for radio transmission
tend to be poor and unpredictable in many office buildings.
[0005] For the reasons stated above, periodic and systematic
maintenance of frequencies for use is required in a radio
transmission network for mobile telephony. In a situation with only
one vendor in a certain geographical region, which means that all
base stations and control equipment originates from the same
provider, several maintenance solutions are conceivable. For
instance a macroscopic solution for handling and monitoring the
communication network including measurement of transmission
properties and maintenance is possible. Using such a macroscopic
tool makes it possible to gather information also from neighbouring
sites and present an optimised network plan. However, an absolute
requirement for presenting the optimised network plan is that
collected information is compatible, and in practice this means
that the entire equipment must be of the same brand, as different
brands build their sites differently and use proprietary
transmission schematics and protocols. Also transmission protocols
between nodes often differ slightly from vendor to vendor, and due
to the increased complexity and competition between vendors, it is
unrealistic the macroscopic tools shall be able to consider all
these additional incompatibilities and difficulties in analytical
manners. Handling the additional complexities associated with
different standards in used communication protocols would require
an immense computational capacity, which is not possible today.
[0006] Hence, there is a need for an improved technique for
handling maintenance of a communication network including tight
frequency planning, in urban or other densely populated
geographical areas.
SUMMARY OF THE INVENTION
[0007] It is therefore an object of this invention to provide an
improved stand-alone tool for the optimisation of frequencies
utilised in a communication network. Another object is to overcome
problems associated with inherent limitations of traditional cell
planning tools. Two examples among others of such tools for cell
and frequency planning are NOX (Network Optimization eXpert) and
FOX (Frequency Optimization eXpert).
[0008] The present invention overcomes the problems associated with
prior art technology by means an apparatus and a method for
measuring interference levels in a telecommunication system
comprising a radio base station communicating with at least one
in-house mounted transceiver, the transceiver defining a
communication range in which it is responsible for handling
communication terminals, such as mobile phones or computer
terminals, characterised in that
[0009] at least one scanner is provided with means for
synchronising with transmitted information from the base station to
the transceiver in a time regime;
[0010] the scanner is connected to measurement means for measuring
the interference level on transmitted information; and
[0011] the measurement means is adapted to compare measured
interference levels with each other and thereby improve
transmission between the base station and the transceiver on a
favourable frequency.
[0012] One of the advantages of the invention is that is provides
the operator with a tool for both setting up a data- and
telecommunication network in the initial phase and after the
establishment, it is a tool for maintenance and periodical
re-planning of the network. In particular the interference
measurements on allocated traffic channels, that are made possible
by means of the invention, are an absolute prerequisite for
performing maintenance of the communication network. The
possibility of comparing interference levels of allocated and
non-allocated traffic channels is beneficial for the operator that
runs a communication network.
[0013] The present invention is therefore beneficial for the
operator in particular. The communication network can be monitored
more closely and the operation of the network can be optimised in
any environment, which is advantageous. Extremely important
positions within the network, sometimes called "hot-spots" can be
provided with additional network capacity, used frequencies can be
less interfered and the strongest of neighbouring sources of
interference can both be found and avoided. By means of the present
invention, the transmission quality in a general sense in a
communication network is enhanced.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] The features, objects, and further advantages of this
invention will become apparent by reading this description in
conjunction with the accompanying drawings, in which like reference
numerals refer to like elements and in which:
[0015] FIG. 1 schematically illustrates an office building with an
in-house communication system according to the present
invention.
[0016] FIG. 2 depicts a flow chart for estimating interference
levels of allocated as well as non-allocated traffic channel
frequencies in order to finding favourable transmission
frequency.
DETAILED DESCRIPTION
[0017] The following description is of the best mode presently
contemplated for practising the invention. The description is not
to be taken in a limiting sense, but is made merely for the purpose
of describing the general principles of the invention. The scope of
the invention should be ascertained with reference to the issued
claims.
[0018] It will be appreciated by those of ordinary skill in the art
that this invention can be embodied in other specific forms without
departing from its essential character. The embodiments described
below should therefore be considered in all respects to be
illustrative and not restrictive. For example, although described
with reference to a GSM system employing a fixed cellular terminal,
the invention is also applicable in other types of communication
systems. These other types of communication systems are for example
GSM (Global System for Mobile communication) combined with any of
the standardised modulation techniques GPRS (General Packet Radio
Service), EDGE (Enhanced Data rates for Global Evolution) or other
future telecommunication standards based on the GSM. Moreover,
measurements of the physical channels, i.e. frequencies like
broadcast control channel carriers, BCCH, and traffic channel
carriers, TCH, are not equal to the logical channels as such.
However, this is readily understood by the person who is skilled in
the art of telecommunication.
[0019] In a digital telephony system for mobile communication based
on TDMA (Time Division Multiple Access), information is transmitted
within certain time slots in a sequence of frames. These frames are
transmitted between handling radio base stations and mobile
terminals, such as cellular phones or other communication means,
and the information conveyed between nodes and terminals may be
either voice traffic or data traffic depending on the nature of the
connection. However, the transmitted information can also be for
control- or synchronisation purposes, which information is
transmitted over so-called control channels and this information
does not interfere with the other kinds of transmitted
information.
[0020] With reference to FIG. 1, a telecommunication system
according to the present invention is depicted. An office building
equipped with in-house mobile telecommunication facilities is
illustrated, which office building is having a radio base station
40 situated at close distance. Well planned in-house mobile
telecommunication equipment is supposed to facilitate higher
transmission rates than the average transmission rates outdoors and
office personnel can be provided with access to corporate
information via wireless LAN (local area network), preferably with
sufficiently high data transmission rates. Therefore, a simplified
office management with improved efficiency can be achieved. Another
advantage is that the office dynamics increases significantly when
installation of electronic equipment and otherwise tedious wiring
is made unnecessary.
[0021] Furthermore with reference to FIG. 1, at least one radio
transceiver 30, 32, 34 for communication with electronic terminals,
such as computers 62 and mobile phones 60, is installed in the
building. According to the illustration, two transceivers are
installed per floor within the whole office building, which
transceivers operate as relaying small sized radio base stations. A
cell 50, 52 is created by each transceiver, which cell is defined
by the space within the building where the transceiver has better
conditions for radio communication with electronic communication
terminals of various kinds than any other transceiver, and thus the
space where the transceiver has the overall responsible for
handling radio transmission to and from terminals. An example with
direct reference to FIG. 1 is cell 64, which cell is handled by the
transceiver 34 and connection is established with the computer
terminal 62. In most cases, the transceivers are in bi-directional
contact with the radio base station 40 via at least one antenna
(not shown), which antenna preferably is placed on the roof of the
office building within line-of-sight to the radio base station for
obtaining a favourable link budget.
[0022] Cells are defined by the transceiver that handles devices
within that particular cell. However, associations of cells can
also be organised. Associations of cells may be organised
analytically, but also in a more empirical way. Cells situated in
office floors near the street level are more interfered by street
level radio transmission than cells of the floors higher up in the
building. Therefore, if cells are to be associated for common
treatment because their conditions for radio transmission are
similar, the associations of cells have to be made with regards to
the positions of the cells respectively. Generally, an association
70 near the street level is made of only a few cells, for instance
those of two floors, and an association 80 higher up in the
building is made of a larger number of cells, for example as shown
in FIG. 1 with eight separate cells of four floors. At least one
radio frequency scanner 10, 14 is placed in each cell association.
The at least one radio frequency scanner is placed inside the
association where the interference reaches its maximum, i.e. as
near corners or other projections of the building as possible. The
scanner, or scanners if applicable, is located where the
interference reaches its maximum to be able to measure the
interference levels from a so-called worst-case perspective. The
scanner is a tool for supervising the interference situation and
thereby support when analysing the neighbour relations. Connected
to the radio frequency scanner is a number of various instruments
such as a scanner manager and tools for measurement, evaluation and
presentation.
[0023] In the following, many notations of channels and codes are
made while referring to GSM standards. Those standards are open
source information well-known and understood be the person skilled
in the art of telecommunication systems. However, and mainly for
clarity reasons, explanations are added to certain specifications
of this text where appropriate. Important to keep in mind is that
all measurements are carried out on a burst level. Neighbour
relations are found by first identifying the strongest broadcast
control channels, BCCHs, and then decoding the cell global
identity, CGI. The strongest broadcast control channels in terms of
signal strength are considered to be the strongest frequencies at
which the base station identity code, BSIC, can be decoded. When
gathering interference data and presenting the interference
situation, it is important that the output gives a true picture of
the interference and that the values presented are stable. This
stability is achieved by filtering the interference values before
the presentation. The filter used for filtering the interference
values may for instance be an exponential recursive filter.
[0024] For the interference measurement system to be functional,
the interference situation must be measured and compared in a
similar fashion for all relevant frequencies, i.e. both for
allocated frequencies and non-allocated frequencies. The
interference situation on non-allocated frequencies is found in a
straightforward manner by measuring the transmitted signal
strength, SS, directly. However, measuring allocated frequencies,
like for instance frequencies of broadcast control channels, BCCHs,
and traffic channels, TCHs, is not as simple, because of the
transmitted wave energy originating from both interference signal
strength and carrier wave signal strength.
[0025] In the case of broadcast control channels BCCHs, which
channels are transmitting continuously, the interference can be
identified by measuring both the signal strength, SS, and the
carrier to interference ratio, C/I, on a burst level: For measuring
the appropriate bursts, a requirement is that the scanner 10, 12
first has been synchronised with the broadcast control channel,
BCCH, which is subjected to measurement. An approximation for the
interference, I, is: 1 I = SS - C I ( 1 )
[0026] The above methods are not applicable for allocated traffic
channels, TCHs, since allocated TCHs are not transmitting signals
continuously, on which signals the interference situation can be
measured and estimated. Therefore, according to the present
invention, another method is suggested for measuring the
interference on allocated traffic channels. The method will be
described sequentially below with reference to FIG. 2.
[0027] The steps in the flowchart of FIG. 2 starts (S10) with and
inquiry of whether the radio frequency scanner 10, 12 is
synchronised with the broadcast control channel, BCCH. If not, the
scanner synchronises (S30) with the broadcast control channel,
BCCH, and otherwise if it is synchronised, the scanner switches
over (S40) to one traffic channel frequency after the other. The
fact is used that the broadcast control channel, BCCH, is
synchronous with the traffic channels, TCHs. Measurements can be
done on any number of traffic channel frequencies during a
predetermined time period, which time period is set by the
operator. Conceivable measurements to be done are signal strength
(SS), carrier to interference ration (C/I) and decoding of the
training sequence code, TSC. The decoding is done by a one to one
mapping of to the base station colour code, BCC. If applicable,
another mapping can be done by utilising the cell global identity,
CGI, with the corresponding training sequence code, TSC.
Interference is measured (S50) on used traffic channels but is also
measured (S60) on unused traffic channels. These measurements are
followed by an estimation, which is built on the preceding
interference measurements, of whether bursts are recognised (S70)
during the measurements from associated cells, whereby the
applicable relations for interference estimation can be chosen when
evaluating the interference situation of each measurement
respectively.
[0028] In case bursts from an associated cell have been recognised,
the approximate relation (1) stated above is applied (S80) for
obtaining a comparable interference level. Otherwise, i.e. no
bursts from associated cells have been found, the interference
level equals the signal strength, i.e. I=SS can be applied (S90)
when comparing (S100) measured interference levels. More in detail,
the interference should be estimated as being equal to the signal
strength, SS, for measurements without training sequence code, TSC,
and according to the above stated relation (1) if the measurement
contains carrier to interference ratio, C/I, and training sequence
code, TSC.
[0029] Having established comparative interference measurements,
the transmission frequency with having the most favourable signal
properties can be recommended (S110) for use. After this
recommendation of which frequency to use, the sequence ends
(S120).
[0030] A system according to the present invention also measures
and estimates interference levels, whereby a presentation and
recommendation according to the above stated relation (1) is made
possible. The sequence leading to a presentation of the
interference situation generally follows a sequence similar to the
one described above with reference to FIG. 2. Furthermore, by means
of the inventive method and system, the operator of the
communication network is able to evaluate and find the neighbour
cell relations by identifying the strongest neighbours for the at
least one associated cell. The scanners 10, 12 help finding the
most favourable of the transmitted frequencies where the base
station identity code, BSIC, can be decoded. This leads to
subsequent possibilities to decode also the cell global identity,
CGI.
[0031] In theory, the possibility remains that an associated cell
and one of its neighbouring cells has the identical training
sequence codes, TSCs. In such a case, although theoretically, the
scanner 10, 12 would interpret occurring and recognised bursts as
bursts from the own associated cell. Measurements of identical
codes from different sources that could not be separated would be
misleading and therefore the system according to the present
invention is instructed to do the same measurements on the idle.
frame. If also the idle frame would contain bursts with the right
training sequence codes, TSCs, the frequency is excluded from use
and hence, no misleading interference measurements may occur.
* * * * *